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What is the difference between decompress and uncompress? Is there any?


The receiving node has to uncompress/decompress the data.

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decompress -- that's it. –  Kris Jan 31 '12 at 11:31
@Kris Post that! :P –  Alenanno Jan 31 '12 at 11:34
But you would say uncompressed data instead of decompressed data? –  Marc Messing Jan 31 '12 at 11:43
@MarcMessing decompressed is a past participle of the verb decompress. Uncompressed is an adjective. –  Alenanno Jan 31 '12 at 11:56
Until the recent burgeoning of computer terms, un- was hardly ever used with a verb unless the verb had a sense of fastening, attaching or enclosing. (With an adjective, including a past participle, un- was used freely). Compress seems to me to be marginally in this group, so uncompress might have occurred, but I don't believe it did. Uncompressed, on the other hand, was unexceptional. Nowadays all sorts of actions that are not reversible in the real world can be reversed in software, so there are many more verbs with un-. –  Colin Fine Jan 1 '13 at 0:23

4 Answers 4

up vote 16 down vote accepted

decompress — that's it.

Uncompressed = not compressed; may never have been compressed in the first place. Just plain data is uncompressed data in every sense. To specifically refer to that which has undergone the process of decompressing, we would say decompressed data. Looking at it in another way, data before being compressed is uncompressed — that extracted from compressed format is decompressed data.

[Edit-1] Also, per Alenanno,
decompressed is a past participle of the verb decompress. Uncompressed is an adjective.

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Also adding the reference I made above, might help (for nonnative speakers, especially). Feel free to add it to your answer. :) –  Alenanno Jan 31 '12 at 12:05
Great answer. Thanks a lot. –  Marc Messing Jan 31 '12 at 12:13
@Alenanno: Done. I think OP cannot up vote. –  Kris Jan 31 '12 at 12:19
@Kris I can though! :D +1 –  Alenanno Jan 31 '12 at 13:59
Seems the Qt people could learn a thing or two from this answer :P –  George Edison Feb 6 at 0:02

I would think that:
*uncompressed data is data that was never altered
*decompressed data is data that has been compressed, then returned to its original state by the process of decompression.

Decompress and uncompress seem to be used synonymously in the context of computing, although decompress seems to be used more frequently. A search on MSDN for uncompress* returns 731 hits, while decompress* returns 4,450 hits.

Seaching on SO gives similar results. There are

  • 22 questions tagged with uncompress
  • none tagged with uncompression,
  • 651 occurrences of uncompress and
  • 34 occurrences of uncompression.
    Total tag count = 22
    Total word count = 685

In contrast, there are

  • 39 questions tagged with decompress
  • 110 questions tagged with decompression
  • 1,467 occurrences of decompress and
  • 865 occurrences of decompression.
    Total tag count = 149
    Total word count = 2,332
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I landed here because of my condumdrum with 'uncompressable', which is rejected by MS Word spell check in favor of 'incompressable'. After decades in IT I'm astonished to see that all the usual resources come down on the side of 'in-'. I was using the term in the sense of 'data that cannot be usefully compressed'. Never let it be said that I'm incorrectable.

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Microsoft’s ideas about how you should write are incorrigibly bad. Turn all that crap off. –  tchrist Dec 8 '13 at 3:35

Uncompressed data will never be "uncompressed" once it's been compressed — it'll be decompressed.

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Please cite at least one reliable source. –  MετάEd Dec 31 '12 at 21:42

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